Move message routing from CefBrowser to CefFrame (see issue #2498).

This change moves the SendProcessMessage method from CefBrowser to CefFrame and
adds CefBrowser parameters to OnProcessMessageReceived and
OnDraggableRegionsChanged.

The internal implementation has changed as follows:
- Frame IDs are now a 64-bit combination of the 32-bit render_process_id and
  render_routing_id values that uniquely identify a RenderFrameHost (RFH).
- CefFrameHostImpl objects are now managed by CefBrowserInfo with life span tied
  to RFH expectations. Specifically, a CefFrameHostImpl object representing a
  sub-frame will be created when a RenderFrame is created in the renderer
  process and detached when the associated RenderFrame is deleted or the
  renderer process in which it runs has died.
- The CefFrameHostImpl object representing the main frame will always be valid
  but the underlying RFH (and associated frame ID) may change over time as a
  result of cross-origin navigations. Despite these changes calling LoadURL on
  the main frame object in the browser process will always navigate as expected.
- Speculative RFHs, which may be created as a result of a cross-origin
  navigation and discarded if that navigation is not committed, are now handled
  correctly (e.g. ignored in most cases until they're committed).
- It is less likely, but still possible, to receive a CefFrame object with an
  invalid frame ID (ID < 0). This can happen in cases where a RFH has not yet
  been created for a sub-frame. For example, when OnBeforeBrowse is called
  before initiating navigation in a previously nonexisting sub-frame.

To test: All tests pass with NetworkService enabled and disabled.

include/capi/cef_render_process_handler_capi.h

@@ -33,7 +33,7 @@
 // by hand. See the translator.README.txt file in the tools directory for
 // more information.
 //
-// $hash=a3cf58db4b29d7395975ab8d63461b5ea8aad064$
+// $hash=6c6efd722dda7480a5449ef31f1d6d9a16fd3465$
 //
 
 #ifndef CEF_INCLUDE_CAPI_CEF_RENDER_PROCESS_HANDLER_CAPI_H_
@@ -166,6 +166,7 @@ typedef struct _cef_render_process_handler_t {
   int(CEF_CALLBACK* on_process_message_received)(
       struct _cef_render_process_handler_t* self,
       struct _cef_browser_t* browser,
+      struct _cef_frame_t* frame,
       cef_process_id_t source_process,
       struct _cef_process_message_t* message);
 } cef_render_process_handler_t;